Corrosion inhibitors for ferrous metals in aqueous solutions of non-oxidizing acids



United States Patent CORROSION INHIBITORS FOR FERROUS lVIETALS t gunous SOLUTIONS OF NON-OXIDIZING Charles T. Pumpelly and Joseph L. Wasco, Midland,

Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Delaware No Drawing. Application December 28, 1956 Serial No. 631,045

14 Claims. (Cl. 252-855) This invention relates to corrosion inhibitors for use in aqueous solutions of non-oxidizing acids to inhibit the corrosion of ferrous metals by such acids.

The inhibitors of the invention are acetylenic alcohols corresponding to the formula R CHEC-CHrJl-OH wherein the R substituents together contain 4 to 12 carbon atoms and are independently Selected from the group consisting of hydrogen, alkyl radicals containing 1 to 8 carbon atoms and which may be joined together to form a cycloalkyl ring containing 5 to 6 carbon atoms, phenyl and chlorophenyl radicals.

According to the invention an acetylenic alcohol corresponding to the above formula is dissolved or dispersed in the acid the corrosive action of which is to be inhibited.

By aqueous acid we mean a composition comprising acid and water and do not mean to exclude the presence of other substances. By ferrous metals we mean iron, steel, stainless steel and, in general, any metal comprising a major proportion of iron.

Only a small amount of the inhibitor is needed. As little as a few thousandths of 1 percent, based on the aqueous acid, significantly reduces the corrosion of ferrous metals exposed to the acid. The degree of inhibition increases with the concentration of the inhibitor up to a level of about 1 percent. Beyond this point little added protection of the metal is obtained by the use of more inhibitor. We generally prefer to use our inhibitors at a level of about 0.1 to 0.4 percent, this amount being adequate for most purposes.

The inhibitors of the invention are effective not only at ordinary temperatures but also at elevated temperatures. All are effective at 150 degrees and some at 200 degrees F. Moreover, they are effective in various concentrations of acids, even including hydrochloric acid up to 37 percent, that is, commercial concentrated acid.

Applications in which the inhibitors are particularly useful include metal-pickling, cleaning and polishing baths, oil well-acidizing solutions, boiler-cleaning compositions and the like.

The inhibitors of this invention are either commercially available or are easily made from commercially available intermediates.

The alcohols are easily prepared from propargyl bromide and the appropriate carbonyl compound by well known methods, such as that of Henbest et al., J. Chem. Soc., 1949, 2696-2700.

In order to demonstrate the effectiveness of our inhibitors, a series of tests was run in which 0.4 percent of the inhibitor was put into a 10 percent aqueous solution of hydrochloric acid held at 150 degrees F. and a coupon of the metal to be tested was suspended in the solution for 16 hours. Thereafter the coupon was 2,913,408 Patented Nov. 17, 1959 cleaned, dried and weighed to determine the amount of metal dissolved by the acid. The results obtained in a series of such tests in which mild steel was used are shown in the following table.

a In the inhibitors of Examples 7 and 8 the 2 R's are joined to form cyclohexyl and eyclopentyl groups, respectively.

Results similar to those shown in the above table are obtained when other non-oxidizing acids, such as sulfuric, phosphoric and acetic acid, are used instead of hydrochloric acid; when other concentrations of the acid up to the commercial concentrated acid (37 percent) are used; and when other ferrous metals are used instead of mild steel. The inhibitors are also effective at elevated temperatures up to about degrees F.

When the inhibitor is not completely soluble in the aqueous acid in which it is to be used, as when the compounds of Examples 3-6 are desired to be used in amounts exceeding their solubility, it is usually advantageous to incorporate into the inhibitor-acid mixture a small amount of a suitable surfactant whereby the inhibitor is solubilized and/ or dispersed in the acid, thereby greatly increasing its effectiveness. In general, the suitable surfactants are those that are stable in acid media under the conditions of use, the non-ionic surfactants being preferred for this reason.

We claim:

1. An aqueous solution of a non-oxidizing acid containing an effective amount of a corrosion inhibitor consisting solely of a compound corresponding to the formula wherein the R substituents together contain 4 to 12 carbon atoms and are independently selected from the group consisting of hydrogen, phenyl, chlorophenyl, alkyl groups containing 1 to 8 carbon atoms each and parts of a cycloalkyl ring containing 5 to 6 carbon atoms.

2. A solution as defined in claim 1 wherein at least one of the R groups is an alkyl group.

3. A solution as defined in claim 1 wherein the two R substituents are joined to form a cycloalkyl group.

4. A solution as defined in claim 1 wherein the inhibitor is 2-(p-chlorophenyl)-4-pentyn-2-ol.

5. A solution as defined in claim 1 wherein the acid is hydrochloric acid.

6. solution as defined in claim 2 wherein one R is a I i 1 hydrogen and the other is an alkyl group.

7. A solution as defined in claim 2 wherein both R groups are alkyl groups. p

8. A solution as defined in claim 3 wherein the inhibitor is 1-(2-propynyl)cyclohexanol.

9. A solution as defined in claim 3 whereinthe-im hibitor is 1-(2-propynyl)cyclopentanol.

10. A solution as defined in claim 6 wherein the inhibitor is 1-heptyn-4-ol.

11. A solution as defined in claim 7 wherein the in hibitor is 4-methyl-1-heptyn-4-ol.

12. A process for inhibiting the corrosion of ferrous metals in contact with aqueous non-oxidizing acid, said process consisting essentially of maintaining in said acid an efiective amount of a corrosion inhibitor consisting solely of a compound as defined in claim 1."

4 t 13. A process as defined in claim 12 wherein the inhibitor is 1-(2-propynyl)cyclohexanol.

14. A process as defined in claim 13 wherein the acid is hydrochloric acid.

References Cited in the file of this patent 'UNITED STATES PATENTS Mascre May 30, 1939 2,204,597 Humphreys et a1. June 18,1940 2,355,599 Walker Aug. 8, 1944 "2,474,603 Viles et a1. June 28, 1949 2,564,757 Glasebrook Aug. 21, 1951 2,603,622 Berger July 15, 1952 2,806,067 Monroe et al. Sept. 10, 1957 2,814,593

Beiswanger et al. Nov. 26, 1957 

1. AN AQUEOUS SOLUTION OF A NON-OXIDIZING ACID CONCTAINING AN EFFECTIVE AMOUNT OF A CORROSION INHIBITOR CONSISTING SOLELY OF A COMPOUND CORRSPONDING TO THE FORMULA 